select 
p.PORT_CODE as "港コード"
,p.PORT_NAME as "港名"
,i1.AMT  as "入国者数"
,i2.AMT  as "出国者数"
,i1.AMT - i2.AMT  as "差分"
from PORT p 
left join (select i.PORT_CODE,sum(i.AMT) as AMT from IMMIGRATION i,GRP g where i.GROUP_CODE=g.GROUP_CODE and g.GROUP_NAME='外国人' and i.KIND_CODE=110 group by i.PORT_CODE) i1
on p.PORT_CODE=i1.PORT_CODE
left join (select i.PORT_CODE,sum(i.AMT) as AMT from IMMIGRATION i,GRP g where i.GROUP_CODE=g.GROUP_CODE and g.GROUP_NAME='外国人' and i.KIND_CODE=120 group by i.PORT_CODE) i2
on p.PORT_CODE=i2.PORT_CODE
where i1.AMT - i2.AMT > 0
order by "差分" desc
,"港コード" desc